This invention relates to integrated circuit packages (IC-packages); and more particularly, this invention relates to processes for recycling substrates which are integrated into the IC-packages.
Throughout the history of the integrated circuit industry, a common practice has been to enclose integrated circuit chip (IC-chip) in an IC-package. Typically, the IC-package includes a substrate to which an IC-chip is attached by multiple solder balls and a filler layer, and a lid which covers the IC-chip and is sealed onto the substrate. Such an IC-package protects the enclosed IC-chip, which is very delicate, from being damaged.
Also in the prior art, a common practice is to build multi-chip assemblies by interconnecting several different IC-chips on a printed circuit board, where each IC-chip is enclosed in its own IC-package. The substrate in each IC-package includes a plurality of I/O terminals; and electrical signals are sent to and received from the IC-chip which is enclosed in the IC-package thru these I/O terminals.
In order to transfer the electrical signals from the I/O terminals on the substrate to the enclosed IC-chip, the substrate includes patterned electrical conductors which run from the I/O terminals to the enclosed IC-chip. The total number of conductors in the substrate can range widely, depending upon the complexity of the IC-chip that is enclosed.
Today, a single IC-chip often sends and receives over 1,000 signals in parallel. Consequently, the corresponding substrate in an IC-package which holds such an IC-chip must contain over 1,000 conductors. These conductors are microscopic in their size; and thus, the structure of the substrate is quite complex.
When an IC-chip in an IC-package becomes defective or obsolete, the conventional practice in the prior art is to replace the entire IC-package with a new IC-chip in a new IC-package. The original IC-package is simply thrown away in its entirety; or sometimes, any precious metal (such as gold) in the original IC-package is recovered.
However, the package which contains the defective or obsolete IC-chip usually contains a substrate which is completely operable; and that substrate can be quite expensive if the number of interconnections which it provides is large. Thus, when any mass produced product contains defective or obsolete IC-chips, the value of the substrates which hold those IC-chips can easily exceed one million dollars. But, in order to remove the lid and the IC-chip and the filler layer and the solder balls from the substrate in a cost effect manner without causing any damage to the substrate, many detailed technical problems need to be overcome.
For example, if the IC-chip together with the filler layer is simply pulled off of the substrate, then some of the conductors can also be pulled off of the substrate. Also, if the solder balls are simply melted off of the substrate, then atoms of the melted solder can diffuse into the conductors in the substrate to thereby form inter-metallic compounds with the conductors that are brittle and can fracture. Further, if all of the solder balls are removed by any means in their entirety from the substrate, then the remaining bare conductors on the substrate can chemically react with the atmosphere to form oxides which prohibit the conductors from being reattached to another IC-chip.
Accordingly, a primary object of the present invention is to provide a novel cost effective process for recycling a substrate from an IC-package by which the above-described technical problems, and others, are avoided.